Interconnect Structure for Semiconductor Devices

ABSTRACT

A cap layer for a copper interconnect structure formed in a first dielectric layer is provided. In an embodiment, a conductive layer is located within a dielectric layer and a top surface of the conductive layer has either a recess, a convex surface, or is planar. An alloy layer overlies the conductive layer and is a silicide alloy having a first material from the conductive layer and a second material of germanium, arsenic, tungsten, or gallium.

This application is a continuation of U.S. patent application Ser. No.12/902,877, entitled “Interconnect Structure for Semiconductor Devices,”filed on Oct. 12, 2010, which is a continuation of U.S. patentapplication Ser. No. 12/638,022, entitled “Interconnect Structure forSemiconductor Devices,” filed on Dec. 15, 2009, which is a continuationof U.S. patent application Ser. No. 11/738,982, now U.S. Pat. No.7,655,556 B2, entitled “Interconnect Structures for SemiconductorDevices,” filed on Apr. 23, 2007, which claims the benefit of U.S.Provisional Application No. 60/919,650, filed on Mar. 23, 2007, entitled“Cu—M/Cu—MSi Formation Using Si Seed Catalysts,” which applications arehereby incorporated herein by reference.

TECHNICAL FIELD

The present invention relates generally to semiconductors and, moreparticularly, to a cap layer over a conductive layer in a semiconductordevice.

BACKGROUND

Generally, integrated circuits (ICs) comprise electronic components,such as transistors, capacitors, or the like, formed on a substrate. Oneor more metal layers are then formed over the electronic components toprovide connections between the electronic components and to provideconnections to external devices. The metal layers typically comprise aninter-layer dielectric (ILD) layer in which interconnect structures,such as vias and conductive traces, are formed, usually with a single-or dual-damascene process.

The trend in the semiconductor industry is towards the miniaturizationor scaling of integrated circuits, in order to provide smaller ICs andimprove performance, such as increased speed and decreased powerconsumption. While aluminum and aluminum alloys were most frequentlyused in the past for the material of conductive lines in integratedcircuits, the current trend is to use copper for a conductive materialbecause copper has better electrical characteristics than aluminum, suchas decreased resistance, higher conductivity, and a higher meltingpoint.

The change in the conductive line material and insulating materials ofsemiconductor devices has introduced new challenges in the manufacturingprocess. For example, copper oxidizes easily and has a tendency todiffuse into adjacent insulating materials, particularly when a low-Kmaterial or other porous insulator is used for the ILD layer. To reducethese effects, attempts have been made to form a cap layer comprising asingle layer of CoWP and CoB over the copper material. While the CoWPand CoB cap layers help reduce the oxidation and diffusion of the copperinto the surrounding ILD layer, the CoWP and CoB cap layers requirenumerous processing steps and often result in metal residue on thesurface of the ILD layer. These cap layers also exhibit poor resistanceto oxygen and other chemicals, which may result in Rc yield loss andhigh contact resistance.

Accordingly, there is a need for a cap layer that eliminates or reducessurface migration and diffusion of the conductive material into adjacentinsulating materials while being easily and efficiently formed.

SUMMARY

These and other problems are generally solved or circumvented, andtechnical advantages are generally achieved, by preferred embodiments ofthe present invention which provides a cap layer over a conductivematerial in a semiconductor device.

In accordance with an embodiment of the present invention, a method forforming a cap layer is provided. The method comprises forming a firstdielectric layer on a substrate, and an interconnect structure in thefirst dielectric layer. A cap layer is formed over the interconnectstructure such that the cap layer comprises germanium, arsenic,tungsten, or gallium. The cap layer may be formed of a silicide byintroducing silane before, during, or after introduction of a processgas comprising germanium, arsenic, tungsten, or gallium.

In accordance with another embodiment of the present invention, a caplayer comprising a copper alloy is formed over a copper interconnect,the copper alloy comprises germanium, arsenic, tungsten, or gallium. Thecap layer may be formed of a silicide by introducing silane before,during, or after introduction of a process gas comprising germanium,arsenic, tungsten, or gallium.

In accordance with yet another embodiment of the present invention, amethod of providing a copper-metal cap layer is provided. Thecopper-metal cap layer may be formed by forming a copper interconnectstructure in a first dielectric layer and introducing a process gascomprising GeH₄, AsH₃, GaH₃, or WF₆ with a diluent gas comprising He,H₂, or N₂. The cap layer may be formed of a silicide by introducingsilane before, during, or after introduction of a process gas comprisinggermanium, arsenic, tungsten, or gallium.

In accordance with yet another embodiment of the present invention, asemiconductor device comprising a first dielectric layer on a substrate,the first dielectric layer having a conductive layer formed therein, theconductive layer comprising a first material and having a recess, isprovided. An alloy layer is located at least partially within therecess, the alloy layer being an silicide alloy comprising the firstmaterial and a second material, the second material comprisinggermanium, arsenic, tungsten, or gallium.

In accordance with yet another embodiment of the present invention, asemiconductor device comprising a conductive layer within a substrate,the conductive layer comprising a first material and having a first topsurface, the substrate having a second top surface planar to the firsttop surface, is provided. An alloy layer is overlying the conductivelayer, the alloy layer having a third top surface that is planar, thealloy layer being a silicide alloy comprising the first material and asecond material, the second material comprising germanium, arsenic,tungsten, or gallium.

In accordance with yet another embodiment of the present invention, asemiconductor device comprising a first dielectric layer on a substrate,the first dielectric layer having a top surface, is provided. Aconductive layer extends through the dielectric layer, the conductivelayer having a convex surface that extends beyond the top surface, theconductive layer comprising a first material. An alloy layer is locatedconformally to the convex surface, the alloy layer being silicidecomprising the first material and a second material, the second materialcomprising germanium, arsenic, tungsten, or gallium.

It should be appreciated by those skilled in the art that the conceptionand specific embodiment disclosed may be readily utilized as a basis formodifying or designing other structures or processes for carrying outthe same purposes of the present invention. It should also be realizedby those skilled in the art that such equivalent constructions do notdepart from the spirit and scope of the invention as set forth in theappended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIGS. 1-5 are cross-section views of a wafer during various steps of anembodiment of the present invention; and

FIGS. 6-8 are cross-section views of a wafer illustrating variousconfigurations of a cap layer in accordance with embodiments of thepresent invention.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of the presently preferred embodiments arediscussed in detail below. It should be appreciated, however, that thepresent invention provides many applicable inventive concepts that canbe embodied in a wide variety of specific contexts. The specificembodiments discussed are merely illustrative of specific ways to makeand use the invention, and do not limit the scope of the invention.

The present invention will be described with respect to embodiments in aspecific context, namely forming copper interconnects in an intermetaldielectric layer. The invention may also be applied, however, to otherdesigns in which it is desirable to limit contamination betweenmaterials or to increase adhesive qualities of successive layers.

FIGS. 1-5 illustrate cross-section views of a first embodiment of thepresent invention in which a cap layer is formed on a metal layer.Referring first to FIG. 1, a workpiece 100 is provided. The workpiece100 comprises a semiconductor substrate 110 having a first dielectriclayer 112 formed thereon. The semiconductor substrate 110 may comprisesilicon or other semiconductor materials. The semiconductor substrate110 may also include other active components or circuits (not shown).The workpiece 100 may include other conductive layers or othersemiconductor elements, e.g. transistors, diodes, etc.

Generally, the first dielectric layer 112 may be formed, for example, ofa low-K dielectric material, such as silicon oxide, phosphosilicateglass (PSG), borophosphosilicate glass (BPSG), fluorinated silicateglass (FSG), SiO_(x)C_(y), Spin-On-Glass, Spin-On-Polymers, siliconcarbon material, compounds thereof, composites thereof, combinationsthereof or the like, by any suitable method known in the art. In anembodiment, the first dielectric layer 112 comprises an oxide that maybe formed by chemical vapor deposition (CVD) techniques usingtetra-ethyl-ortho-silicate (TEOS) and oxygen as a precursor. Othermaterials and processes may be used. It should also be noted that thefirst dielectric layer 112 may comprise a plurality of dielectriclayers, with or without an etch stop layer formed between adjacentdielectric layers. The first dielectric layer 112 is preferably about500 Å to about 5000 Å in thickness, but more preferably 2000 Å.

An opening 116 is formed in the first dielectric layer 112. The opening116 may be a trench, via, or other pattern into which a conductive layeris to be formed. For example, in an embodiment, the opening 116comprises a long thin trench that is relatively straight, or that curvesand digresses in bends or other patterns to form conductive lines withina metal layer. In other embodiments, the opening 116 forms a via,contact plug, or other interconnect structure electrically coupled toelectrical devices or other conductive lines formed on underlyinglayers.

The opening 116 may be formed by photolithography techniques known inthe art. Generally, photolithography techniques involve applying aphotoresist material (not shown) and exposing the photoresist materialin accordance with a desired pattern. The photoresist material is thendeveloped to remove a portion of the photoresist material, therebyexposing the underlying material in accordance with the desired pattern.The remaining photoresist material protects the underlying material fromsubsequent processing steps, such as etching, performed to form theopening 116 in the first dielectric layer 112. The etching process maybe a wet or dry, anisotropic or isotropic, etch process, but preferablyis an anisotropic dry etch process. After the opening 116 is formed inthe first dielectric layer 112, the remaining photoresist, if any, maybe removed. Other processes, such as electron beam lithography (EBL) orthe like, may be utilized to form the opening 116.

It should be noted that the process discussed above described asingle-damascene process for illustrative purposes only. Otherprocesses, such as a dual-damascene process may be utilized inaccordance with an embodiment of the present invention. For example, adual-damascene process may be utilized to form a trench and a viathrough one or more layers of the first dielectric layer 112.

After the opening 116 is formed, an optional first barrier layer 120 isformed in the opening 116. The first barrier layer 120 may be formed ofone or more adhesion layers and/or barrier layers. In an embodiment, thefirst barrier layer 120 is formed of one or more layers of conductivematerials, such as titanium, titanium nitride, tantalum, tantalumnitride, or the like. In an exemplary embodiment, the first barrierlayer 120 is formed of a thin layer of tantalum nitride and a thin layerof tantalum deposited by CVD techniques. In this embodiment, thecombined thickness of the tantalum nitride and tantalum layers is about50 Å to about 500 Å.

A conductive layer 122 is formed in the opening on the optional firstbarrier layer 120. The opening 116 may be filled with the conductivematerial by, for example, performing a blanket deposition process to athickness such that the opening 116 is at least substantially filled.The conductive layer 122 may comprise metals, elemental metals,transition metals, or the like. In an exemplary embodiment, theconductive layer 122 is copper. The conductive layer 122 may also beformed by depositing a seed layer and performing an electro-chemicalplating process.

A planarization process, such as a chemical-mechanical process (CMP),may be performed to planarize the surface and to remove excess depositsof the material used to form the first barrier layer 120 and theconductive layer 122 as illustrated in FIG. 1.

Furthermore, a preclean process may be performed to remove impuritiesalong the surface of the conductive layer 122. The pre-clean process maybe a reactive or a non-reactive pre-clean process. For example, areactive process may include a plasma process using ahydrogen-containing plasma, and a non-reactive process may include aplasma process using an argon-containing or helium-containing plasma.The pre-clean process may also be a plasma process using a combinationof the above gases.

In an embodiment in which the conductive layer 122 comprises copper, thepre-clean process may be performed using an H₂ plasma, such as N₂NH₃,NH₃, or the like, under a pressure of about 1 mTorr to about 10 Torr anda temperature of about 250° C. to about 400° C. Other processes andmaterials may be used.

FIG. 2 illustrates the workpiece 100 after a cap layer 210 has beenformed in accordance with an embodiment of the present invention. In anembodiment, the cap layer 210 comprises a copper-metal alloy. One ofordinary skill in the art will realize that the process described hereinmay be performed by in-situ deposition and does not necessarily requireadditional tools or equipment. Because of this, the cap layer 210 may beformed quickly and efficiently, thereby reducing costs.

For example, a cap layer 210 comprising a copper germanium alloy may beformed by introducing a process gas of GeH₄ with a diluent gas, such asHe, H₂, N₂, or the like, at a ratio between about 1:100 to about 1:10, apressure of about 1 mTorr to about 10 Torr, and a temperature of about250° C. to about 400° C. As another example, a cap layer 210 comprisinga copper arsenic alloy may be formed by introducing a process gas suchas AsH₃, ASCl₃, or the like with a diluent gas, such as He, H₂, N₂, orthe like, at a ratio between about 1:100 to about 1:10, a pressure ofabout 1 mTorr to about 10 Torr, and a temperature of about 250° C. toabout 400° C. In yet another example, a cap layer 210 comprising acopper tungsten alloy may be formed by introducing a process gas such asWF₆, W(Co)₆ or the like with a diluent gas, such as He, H₂, N₂, or thelike, at a ratio between about 1:100 to about 1:10, a pressure of about1 mTorr to about 10 Torr, and a temperature of about 250° C. to about400° C. In yet another example, a cap layer 210 comprising a coppergallium alloy may be formed by introducing a process gas such as GaH₃ orthe like with a diluent gas, such as He, H₂, N₂, or the like, at a ratiobetween about 1:100 to about 1:10, a pressure of about 1 mTorr to about10 Torr, and a temperature of about 250° C. to about 400° C.

In another embodiment, the cap layer 210 comprises a copper-metalsilicide material. In this embodiment, silane (SiH₄) may be introducedbefore, during, or after the introduction of the process gas. Theintroduction of silane causes the selective formation of a silicon seedlayer on the exposed copper of the interconnect structure and causes theformation of a copper-metal silicide cap layer. Generally, the seedlayer (such as seed layer 211 illustrated in FIG. 2) comprises a thinatomic layer of a material to aid in the formation a thicker layer.

In an embodiment, the seed layer comprises a silicon seed layer formedby introducing SiH₄ or a silane-based gas (e.g., SiH₆) for a time periodof about 4 seconds to about 10 seconds at a temperature of about 250° C.to about 400° C. prior to the introduction of a metal precursor. Adissociation process occurs that results in a thin atomic silicon seedlayer being selectively deposited on the conductive layer 122.Thereafter, the metal precursor gas is introduced to form thecopper-metal silicide cap layer 210. For example, a cap layer 210comprising a copper germanium silicide may be formed by introducing aprocess gas of GeH₄, with a diluent gas, such as He, H₂, N₂, or thelike, at a ratio of process gas mixture to diluent gas of between about1:100 to about 1:10, a pressure of about 1 mTorr to about 10 Torr and atemperature of about 250° C. to about 400° C.

As another example, a cap layer 210 comprising a copper arsenic silicidemay be formed by introducing a process gas of AsH₃ with a diluent gas,such as He, H₂, N₂, or the like, at a ratio of process gas mixture todiluent gas of between about 1:100 to about 1:10, a pressure of about 1mTorr to about 10 Torr and a temperature of about 250° C. to about 400°C. In yet another example, a cap layer 210 comprising a copper tungstensilicide may be formed by introducing a process gas of WH₆ with adiluent gas, such as He, H₂, N₂, or the like, at a ratio of process gasmixture to diluent gas of about 1:100 to about 1:10, a pressure of about1 mTorr to about 10 Torr and a temperature of about 250° C. to about400° C. In yet another example, a cap layer 210 comprising a coppergallium silicide may be formed by introducing a process gas of GaH₃ witha diluent gas, such as He, H₂, N₂, or the like, at a ratio of processgas mixture to diluent gas of about 1:100 to about 1:10, a pressure ofabout 1 mTorr to about 10 Torr and a temperature of about 250° C. toabout 400° C.

In yet another embodiment, a copper-metal silicide cap layer may beformed by simultaneously introducing a mixture of silane and a metalprecursor. For example, a cap layer 210 comprising a copper germaniumsilicide may be formed by introducing a process gas mixture of GeH₄ andSiH₄ at a ratio GeH₄ to SiH₄ of between about 1:1 to about 1:100, with adiluent gas, such as He, H₂, N₂, or the like, at a ratio of process gasmixture to diluent gas of between about 1:100 to about 1:10, a pressureof about 1 mTorr to about 10 Torr and a temperature of about 250° C. toabout 400° C. In this manner, the silicon of the SiH₄ selectively reactswith the cap layer 210 to form a metal silicide.

As another example, a cap layer 210 comprising a copper arsenic silicidemay be formed by introducing a process gas mixture of AsH₃ and SiH₄ at aratio of AsH₃ to SiH₄ of between about 1:1 to about 1:100 with a diluentgas, such as He, H₂, N₂, or the like, at a ratio of process gas mixtureto diluent gas of between about 1:100 to about 1:10, a pressure of about1 mTorr to about 10 Torr and a temperature of about 250° C. to about400° C. In yet another example, a cap layer 210 comprising a coppertungsten silicide may be formed by introducing a process gas mixture ofWF₆ and SiH₄ at a ratio of WH₆ to SiH₄ of between about 1:1 to about1:10, with a diluent gas, such as He, H₂, N₂, or the like, at a ratio ofprocess gas mixture to diluent gas of about 1:100 to about 1:10, apressure of about 1 mTorr to about 10 Torr and a temperature of about250° C. to about 400° C. In yet another example, a cap layer 210comprising a copper gallium silicide may be formed by introducing aprocess gas mixture of GaH₃ and SiH₄ at a ratio of GaH₃ to SiH₄ ofbetween about 1:1 to about 1:100, with a diluent gas, such as He, H₂,N₂, or the like, at a ratio of process gas mixture to diluent gas ofabout 1:100 to about 1:10, a pressure of about 1 mTorr to about 10 Torrand a temperature of about 250° C. to about 400° C.

In yet another embodiment, a cap layer 210 comprising a copper-metalsilicide may be formed by introducing silane gas after the introductionof a metal precursor. For example, a cap layer 210 comprising a coppergermanium silicide may be formed by introducing a process gas of GeH₄,with a diluent gas, such as He, H₂, N₂, or the like, at a ratio ofprocess gas mixture to diluent gas of between about 1:100 to about 1:10,a pressure of about 1 mTorr to about 10 Torr and a temperature of about250° C. to about 400° C., and then introducing silane for a time periodof about 4 seconds to about 10 seconds at a pressure of about 1 mTorr toabout 10 Torr and a temperature of about 250° C. to about 400° C.

As another example, a cap layer 210 comprising a copper arsenic silicidemay be formed by introducing a process gas of AsH₃ with a diluent gas,such as He, H₂, N₂, or the like, at a ratio of process gas mixture todiluent gas of between about 1:100 to about 1:10, a pressure of about 1mTorr to about 10 Torr and a temperature of about 250° C. to about 400°C., and then introducing silane for a time period of about 4 seconds toabout 10 seconds at a pressure of about 1 mTorr to about 10 Torr and atemperature of about 250° C. to about 400° C. In yet another example, acap layer 210 comprising a copper tungsten silicide may be formed byintroducing a process gas of WF₆ with a diluent gas, such as He, H₂, N₂,or the like, at a ratio of process gas mixture to diluent gas of about1:100 to about 1:10, a pressure of about 1 mTorr to about 10 Torr and atemperature of about 250° C. to about 400° C., and then introducingsilane for a time period of about 4 seconds to about 10 seconds at apressure of about 1 mTorr to about 10 Torr and a temperature of about250° C. to about 400° C. In yet another example, a cap layer 210comprising a copper gallium silicide may be formed by introducing aprocess gas of GaH₃ with a diluent gas, such as He, H₂, N₂, or the like,at a ratio of process gas mixture to diluent gas of about 1:100 to about1:10, a pressure of about 1 mTorr to about 10 Torr and a temperature ofabout 250° C. to about 400° C., and then introducing silane for a timeperiod of about 4 seconds to about 10 seconds at a pressure of about 1mTorr to about 10 Torr and a temperature of about 250° C. to about 400°C.

FIG. 3 illustrates the workpiece 100 after an optional etch stop layer310 has been formed thereon in accordance with an embodiment of thepresent invention. In an embodiment, a pre-treatment process isperformed prior to the formation of the etch stop layer 310. Thepre-treatment process may be a plasma process using H₂, N₂NH₃, a mixtureof H₂/N₂H₃, or the like at a flow rate of about 100 sccm to about 30000sccm at a pressure of about 1 mTorr to about 100 mTorr and at power ofabout 200 Watts to about 1000 Watts and at a temperature of about 275°C. to about 400° C., for example.

Thereafter, the etch stop layer 310 may be formed on the surface of thefirst dielectric layer 112. The etch stop layer 310 is preferably formedof a dielectric material having a different etch selectivity fromadjacent layers. In an embodiment, the etch stop layer 310 may be formedof SiCN, SiCO, CN, BCN, combinations thereof, or the like deposited byCVD or PECVD to a thickness of about 0 Å to about 800 Å, but morepreferably about 100 Å. The etch stop layer 310 protects the underlyingstructures, such as the first dielectric layer 112, and also providesimproved adhesion for subsequently formed layers.

FIG. 4 illustrates the workpiece 100 after a second dielectric layer 410has been formed in accordance with an embodiment of the presentinvention. The second dielectric layer 410 may be formed, for example,of a low-K dielectric material, such as silicon oxide, phosphosilicateglass (PSG), borophosphosilicate glass (BPSG), fluorinated silicateglass (FSG), SiO_(x)C_(y), Spin-On-Glass, Spin-On-Polymers, siliconcarbon material, compounds thereof, composites thereof, combinationsthereof or the like, by any suitable method known in the art. In anembodiment, second dielectric layer 410 comprises a material similar tothe first dielectric layer 112, such as an oxide that may be formed bychemical vapor deposition (CVD) techniques usingtetra-ethyl-ortho-silicate (TEOS) and oxygen as a precursor. Othermaterials and processes may be used. It should also be noted that thesecond dielectric layer 410 may comprise a plurality of dielectriclayers, with or without an etch stop layer formed between adjacentdielectric layers. The second dielectric layer 410 is preferably about1000 Å to about 6000 Å in thickness, but more preferably 3000 Å.

FIG. 5 illustrates the workpiece 100 without the optional etch stoplayer 310 (see FIG. 3) in accordance with an embodiment of the presentinvention. In this embodiment, the first dielectric layer 112 and thesecond dielectric layer 410 may comprise the same type of material ordifferent materials.

It should be noted that the embodiments illustrated in FIGS. 1-5illustrate the cap layer 210 having a top surface that is coplanar witha top surface of the first dielectric layer 112 for illustrativepurposes only. The conductive layer 122 may take any shape, and beformed using a single or dual damascene process.

For example, FIGS. 6-8 illustrate other shapes for the conductive layer122 and the cap layer 210. In particular, FIG. 6 illustrates theconductive layer 122 having a recess, FIG. 7 illustrates the cap layer210 protruding above a surface of the first dielectric layer 112, andFIG. 8 illustrates the conductive layer 122 protruding above a surfaceof the first dielectric layer 112. Other configurations may be used.

One of ordinary skill in the art will realize that embodiments of thepresent invention may be utilized to form interconnections exhibitinglower line-to-line (L-L) leakage with materials coherent to currentback-end-of-line (BEOL) processing materials. Furthermore, themetal/metal silicide cap layers disclosed herein exhibit improvedintegrity with less voids between the cap and the etch stop layer, andat a lower cost. The electromigration (EM) and time-dependent dielectricbreakdown (TDDB) characteristics may also be improved.

Although the present invention and its advantages have been described indetail, it should be understood that various changes, substitutions andalterations can be made herein without departing from the spirit andscope of the invention as defined by the appended claims. For example,different types of materials and processes may be varied while remainingwithin the scope of the present invention.

Moreover, the scope of the present application is not intended to belimited to the particular embodiments of the process, machine,manufacture, composition of matter, means, methods and steps describedin the specification. As one of ordinary skill in the art will readilyappreciate from the disclosure of the present invention, processes,machines, manufacture, compositions of matter, means, methods, or steps,presently existing or later to be developed, that perform substantiallythe same function or achieve substantially the same result as thecorresponding embodiments described herein may be utilized according tothe present invention. Accordingly, the appended claims are intended toinclude within their scope such processes, machines, manufacture,compositions of matter, means, methods, or steps.

What is claimed is:
 1. A semiconductor device comprising: a firstdielectric layer on a substrate, the first dielectric layer having aconductive layer formed therein, the conductive layer comprising a firstmaterial and having a recess; and an alloy layer at least partiallywithin the recess, the alloy layer being a silicide alloy comprising thefirst material and a second material, the second material comprisinggermanium, arsenic, tungsten, or gallium.
 2. The semiconductor device ofclaim 1, further comprising a seed layer between the conductive layerand the alloy layer.
 3. The semiconductor device of claim 1, wherein thefirst material comprises copper.
 4. The semiconductor device of claim 1,further comprising a second dielectric layer directly over the alloylayer.
 5. The semiconductor device of claim 1, further comprising: anetch stop layer over the alloy layer and the first dielectric layer, anda second dielectric layer over the etch stop layer.
 6. The semiconductordevice of claim 1, further comprising a barrier layer interposed betweenthe conductive layer and sidewalls of the first dielectric layer.
 7. Thesemiconductor device of claim 6, wherein the alloy layer extends overthe barrier layer.
 8. A semiconductor device comprising: a conductivelayer within a substrate, the conductive layer comprising a firstmaterial and having a first top surface, the substrate having a secondtop surface planar to the first top surface; and an alloy layeroverlying the conductive layer, the alloy layer having a third topsurface that is planar, the alloy layer being a silicide alloycomprising the first material and a second material, the second materialcomprising germanium, arsenic, tungsten, or gallium.
 9. Thesemiconductor device of claim 8, further comprising a seed layer betweenthe conductive layer and the alloy layer.
 10. The semiconductor deviceof claim 8, wherein the first material comprises copper.
 11. Thesemiconductor device of claim 8, further comprising a second dielectriclayer directly over the alloy layer.
 12. The semiconductor device ofclaim 8, further comprising: an etch stop layer over the alloy layer andthe substrate, and a second dielectric layer over the etch stop layer.13. The semiconductor device of claim 8, further comprising a barrierlayer interposed between the conductive layer and sidewalls of thesubstrate.
 14. The semiconductor device of claim 8, wherein thesubstrate comprises a low-k dielectric.
 15. A semiconductor devicecomprising: a first dielectric layer on a substrate, the firstdielectric layer having a top surface; a conductive layer extendingthrough the dielectric layer, the conductive layer having a convexsurface that extends beyond the top surface, the conductive layercomprising a first material; and an alloy layer located conformally tothe convex surface, the alloy layer being a silicide and comprising thefirst material and a second material, the second material comprisinggermanium, arsenic, tungsten, or gallium.
 16. The semiconductor deviceof claim 15, further comprising a seed layer between the conductivelayer and the alloy layer.
 17. The semiconductor device of claim 15,wherein the first material comprises copper.
 18. The semiconductordevice of claim 15, further comprising a second dielectric layerdirectly over the alloy layer.
 19. The semiconductor device of claim 15,further comprising a barrier layer interposed between the conductivelayer and sidewalls of the first dielectric layer.
 20. The semiconductordevice of claim 19, wherein the alloy layer extends over the barrierlayer.